转-Cannot refer to an instance field arg while explicitly invoking a constructor

Posted 2020-09-17 止 静

 

编译失败：

Cannot refer to an instance field arg while explicitly invoking a constructor  调用方法是不能引用一个实例变量

 

 1 package arkblue.lang.javapuzzler.n53;
 2 
 3 class Thing {
 4     public Thing(int i) {
 5 
 6     }
 7 }
 8 
 9 public class MyThing extends Thing {
10     private final int arg;
11 
12     public MyThing() {
13         super(arg = Math.round(12L)); //编译失败
14     }
15 
16 }

解决办法:使用了交替构造器调用机制（alternate constructor invocation）

在这个私有构造器中，表达式SomeOtherClass.func()的值已经被捕获到了变量i中，并且它可以在超类构造器返回之后存储到final类型的域arg中

 1 class SomeOtherClass {
 2     static int func() {
 3         return Math.round(12L);
 4     }
 5 }
 6 
 7 public class MyThing extends Thing {
 8     private final int arg;
 9 
10     public MyThing() {
11         this(SomeOtherClass.func());
12     }
13 
14     private MyThing(int i) {
15         super(i);
16         arg = i;
17     }
18 }